matroskadec: partly revert "demux relevant subtitle packets after a seek"

This reverts parts of c1658257. The hard
coded 30 seconds are a lot, and finishing the seek can takes several
seconds when the source is on a network share. Remove this code
entirely, because it does more bad than good.

(Commit message provided by committer, based on the original messages
by the patch author.)
Signed-off-by: Rainer Hochecker <fernetmenta@online.de>
Signed-off-by: wm4 <nfxjfg@googlemail.com>

libavformat/matroskadec.c

@@ -3399,18 +3399,6 @@ static int matroska_read_seek(AVFormatContext *s, int stream_index,
         tracks[i].audio.sub_packet_cnt = 0;
         tracks[i].audio.buf_timecode   = AV_NOPTS_VALUE;
         tracks[i].end_timecode         = 0;
-        if (tracks[i].type == MATROSKA_TRACK_TYPE_SUBTITLE &&
-            tracks[i].stream &&
-            tracks[i].stream->discard != AVDISCARD_ALL) {
-            index_sub = av_index_search_timestamp(
-                tracks[i].stream, st->index_entries[index].timestamp,
-                AVSEEK_FLAG_BACKWARD);
-            while (index_sub >= 0 &&
-                  index_min > 0 &&
-                  tracks[i].stream->index_entries[index_sub].pos < st->index_entries[index_min].pos &&
-                  st->index_entries[index].timestamp - tracks[i].stream->index_entries[index_sub].timestamp < 30000000000 / matroska->time_scale)
-                index_min--;
-        }
     }
 
     avio_seek(s->pb, st->index_entries[index_min].pos, SEEK_SET);